trouble with smooth shading 2.8
You may have face normals facing the wrong way in that stripe along the front of the face. Try recalculating them outside and it might go away. 

You can show normals in blender 2.8 by clicking on the overlays menu in the 3d viewport



You can recalculate the normals on the outside of the mesh with Shift+N if that truly is your issue.

Note that you can only recalculate normals on geometry that you have selected, so go to face mode, then select all with A before you use the shortcut.